CA2533428A1 - High-strength alloy for heat exchangers - Google Patents
High-strength alloy for heat exchangers Download PDFInfo
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- CA2533428A1 CA2533428A1 CA002533428A CA2533428A CA2533428A1 CA 2533428 A1 CA2533428 A1 CA 2533428A1 CA 002533428 A CA002533428 A CA 002533428A CA 2533428 A CA2533428 A CA 2533428A CA 2533428 A1 CA2533428 A1 CA 2533428A1
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- Prior art keywords
- aluminium alloy
- aluminium
- strip
- heat exchangers
- cold
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 10
- 239000000956 alloy Substances 0.000 title claims abstract description 10
- 229910000838 Al alloy Inorganic materials 0.000 claims abstract description 58
- 239000004411 aluminium Substances 0.000 claims abstract description 40
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 40
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 40
- 238000004519 manufacturing process Methods 0.000 claims abstract description 15
- 238000005219 brazing Methods 0.000 claims description 40
- 238000000034 method Methods 0.000 claims description 23
- 238000005096 rolling process Methods 0.000 claims description 18
- 238000005275 alloying Methods 0.000 claims description 17
- 229910052749 magnesium Inorganic materials 0.000 claims description 14
- 238000005098 hot rolling Methods 0.000 claims description 13
- 230000032683 aging Effects 0.000 claims description 12
- 229910000679 solder Inorganic materials 0.000 claims description 10
- 229910052710 silicon Inorganic materials 0.000 claims description 8
- 229910052802 copper Inorganic materials 0.000 claims description 7
- 238000005266 casting Methods 0.000 claims description 6
- 238000005097 cold rolling Methods 0.000 claims description 5
- 238000000137 annealing Methods 0.000 claims description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 2
- 239000010703 silicon Substances 0.000 claims description 2
- 239000011261 inert gas Substances 0.000 abstract description 11
- 229910052804 chromium Inorganic materials 0.000 abstract description 2
- 229910052748 manganese Inorganic materials 0.000 abstract description 2
- 229910052725 zinc Inorganic materials 0.000 abstract description 2
- 238000003466 welding Methods 0.000 abstract 2
- 239000012535 impurity Substances 0.000 abstract 1
- 239000011777 magnesium Substances 0.000 description 15
- 230000004907 flux Effects 0.000 description 14
- 239000010949 copper Substances 0.000 description 12
- 238000005260 corrosion Methods 0.000 description 8
- 230000007797 corrosion Effects 0.000 description 8
- 229910052792 caesium Inorganic materials 0.000 description 7
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical compound [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 description 7
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 6
- 238000001816 cooling Methods 0.000 description 6
- 238000000265 homogenisation Methods 0.000 description 6
- 239000011651 chromium Substances 0.000 description 4
- 239000011572 manganese Substances 0.000 description 4
- 230000009972 noncorrosive effect Effects 0.000 description 4
- 238000005253 cladding Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 230000004888 barrier function Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 239000011701 zinc Substances 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- 229910019752 Mg2Si Inorganic materials 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 238000004378 air conditioning Methods 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000004320 controlled atmosphere Methods 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 239000011162 core material Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005247 gettering Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
- 238000009736 wetting Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/02—Making non-ferrous alloys by melting
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C21/00—Alloys based on aluminium
- C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
- C22C21/08—Alloys based on aluminium with magnesium as the next major constituent with silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C21/00—Alloys based on aluminium
- C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
- C22F1/047—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with magnesium as the next major constituent
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
- C22F1/05—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys of the Al-Si-Mg type, i.e. containing silicon and magnesium in approximately equal proportions
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Metal Rolling (AREA)
- Conductive Materials (AREA)
- Laminated Bodies (AREA)
Abstract
The invention relates to a cold-hardened aluminium alloy for heat exchangers, a method for production of a cold-hardened aluminium strip or sheet and an aluminium strip or sheet. According to the invention, a cold-hardened aluminium alloy for heat exchangers may be provided which permits an economic application of inert gas shielded welding for the production of heat exchangers and with high resistance after a natural hardening after the welding, whereby the aluminium alloy has the following alloy components in wt.
%: Si <= 0.7%, 0.1% <= Mg <= 1, Fe <= 0.3%, 0.08% <= Cu <= 0.2%, Ti <= 0.2%, Mn <= 0.1%, Cr <= 0.1%, Zn <= 0.1%, unavoidable impurities individually max.
0.1%, in total max. 0.15% and remainder aluminium.
%: Si <= 0.7%, 0.1% <= Mg <= 1, Fe <= 0.3%, 0.08% <= Cu <= 0.2%, Ti <= 0.2%, Mn <= 0.1%, Cr <= 0.1%, Zn <= 0.1%, unavoidable impurities individually max.
0.1%, in total max. 0.15% and remainder aluminium.
Description
GS 030029~~10 HIGH-STRENGTH ALLOY FOR HEAT EXCI-IANGERS
The invention relates to a cold age-hardenable aluminium alloy for heat exchangers, a method for producing a cold age-hardenable aluminium strip and an aluminium strip or sheet.
Heat exchangers consisting of aluminium or aluminium alloys are increasingly being used in the automobile field. In this case, the use of aluminium instead of the previously commonly used nonferrous metal heat exchangers has almost halved the weight of heat exchangers with comparable size and performance. Heat exchangers of aluminium or an aluminium alloy are nowadays used in the motor vehicle mainly for cooling the cooling water, oil and in air-conditioning systems. Heat exchangers f or motor vehicles are usually made of aluminium strips or sheets, the individual pre-fabricated components of the heat exchanger such as fins, tubes and distributors for example, being joined together by brazing. The loads acting in practical use on components thus manufactured and built into motor vehicles as a result of intermittent vibrations, more sustained vibrations, corrosion attack and similar are considerable. This particularly applies to the fins via which the heat is removed. Despite the considerable loads and increasing operating pressures of the heat exchangers in motor vehicles, there continues to be a trend towards saving weight in motor vehicles and therefore towards a further reduction in the wall thickness of the heat exchanger. However, this results in further increasing strength requirements for the aluminium alloy of the heat exchangers, especially after brazing. On the one hand, vacuum brazing without flux and inert-gas brazing using non-corrosive fluxes are available for brazing heat exchangers. The cold age-hardenable aluminium alloys used so far for the vacuum brazing of heat exchangers, for example, the aluminium alloy AA6063 (AlMgO, ?Si), AA6061 (AlMglSiCu) or AA6951 (AlMgO, 6SiCu), have relatively high magnesium contents in order, on the one hand, to prevent any oxidation of the molten aluminium solder on the components to be brazed as a result of "gettering" during the brazing process in vacuum and thereby ensure a perfect brazed joint without flux and on the other hand, to achieve high strength values of the brazed heat exchangers during natural ageing after brazing. A disadvantage with this method however is that it is cost-intensive to maintain the gas protection and the purity requirement for the components to be soldered. The alternative inert-gas brazing (also called CAB - controlled atmosphere brazing) certainly requires less expenditure under these aspects and additionally makes it possible to achieve up to 200 shorter brazing cycles but it is not possible to use the aluminium alloy having high magnesium contents known from vacuum brazing since the magnesium reacts with the non-corrosive fluxes during the brazing. This can only be prevented by using more expensive caesium-containing fluxes. It is furthermore possible to use high-copper-content aluminium alloys (Cu content > 0.50) which however tend to form heat cracks during casting and thus impose increased requirements on the casting of the rolling bars which should be considered to be critical from economic aspects. In addition, at elevated Cu i contents there is a risk of sensitivation for pitting or grain-boundary corrosion if copper is present in suitably precipitated form in the structure. Finally, in i:~ert-gas brazing an aluminium alloy with an intermediate cladding can be used as a diffusion barrier layer so that a cold age-hardenable aluminium alloy with relatively high magnesium contents is used as core material. Howev a r, intermediate cladding with a diffusion barrier lave r is associated with additional costs so that economica 1 production of heat exchangers likewise cannot be achieved.
The fabrication of heat exchangers by brazing of components consisting of the aforementioned aluminium alloys is known, for example, from US Patent Specification US 4,214,925.
Starting from the previously indicated prior art, it is thus the object of the present invention to provide a cold age-hardenable aluminium alloy for heat exchangers, a method for producing an aluminium strip for heat exchangers and a corresponding aluminium strip or sheet which has high strength values after natural agein g following brazing.
According to a first teaching of the present invention, the object derived and indicated above is solved f or an aluminium alloy by said aluminium alloy having the following alloying components in wt. o:
Si -<< 0.70 0.1% <- Mg < 1%
Fe <-0.30 0.080 < Cu < 0.20 Ti -<0.20 Mn -<<0.1%
Cr <-0.1o ~n <- 0.1%, unavoidable accompanying elements individually to a maximum of O.lo and in total to a maximum of 0.150 and aluminium as the remainder.
It has surprisingly been shown that heat exchangers consisting of an aluminium alloy containing the alloying fractions specified above, after natural ageing at room temperature following brazing, have the necessary strength for use in motor vehicles, especially the yield point RP~;,2, without further heat treatments being necessary. The reason for this is the combination of the Si and Mg contents according to the invention which form finely distributed precipitates of the type Mg2Si in the aluminium alloy according to the invention and result in an increase in strength as a result of natural ageing at room temperature. This increase in strength by natural ageing is further improved by adding copper in the claimed range of 0.08 wt.o to 0.2 wt. o.
Limiting the Fe content to a maximum of 0.3 wt.% ensures that Si is present in the aluminium alloy in a dissolved state. Furthermore, the low Cu contents of 0.2 wt.o maximum on the one hand ensure that the increase in strength during natural ageing can be increased and on the other hand, this limitation of the Cu content reduces the sensitivity of the strength of the aluminium alloy to the cooling rate after brazing. Likewise, the Mn content must be limited to a maximum of 0.1 wt.o to limit the dependence of the strength of the aluminium alloy on the cooling rate after brazing. In contrast, Cr contents of 0.1 wt.o maximum increase the strength and the corrosion resistance of the aluminium alloy according to the invention. In addition, a Ti content of 0.2 wt.% maximum has a positive effect on the resistance to corrosion of the aluminium alloy according to the invention since the Ti alloying element contributes to the grain refining of the structure of the aluminium alloy and thus makes the corrosion attack uniform. In order to avoid the negative effect of zinc on the corrosion of the aluminium alloy according to the invention, the 2n content must be restricted to a maximum of 0.1 wt. o.
According to a first advantageous embodiment, the strength of the aluminium alloy according to the invention can be further increased by natural ageing after brazing by the aluminium alloy containing Si, Mg and Cu as the principal alloying elements.
In order to avoid softening of the components of a heat exchanger to be brazed during brazing, it is advantageous for carrying out a perfect brazing process if the solidus temperature of the aluminium alloy does not go below 610°C
since brazing is usually carried out at temperatures up to 600°C. According to the invention this is achieved by the total of the alloying fractions of Si, Mg and Cu not exceeding 1.2 wt. o. In this-case, alloying elements generally bring about a reduction in the solidus temperature where Si causes a reduction in the solidus temperature of the aluminium alloy a factor of 1.2 greater than Mg and Mg in turn causes a reduction in the solidus temperature a factor of 3.5 more effective than Cu.
This does not apply to the alloying element Ti so that an increase in the solidus temperature of the aluminium alloy according to the invention can be achieved b y the aluminium alloy having Ti as an alloying component.
If the upper limit of the claimed alloy is exhauste d for magnesium, the brazing of heat exchangers fabricate d from this alloy is preferably effected by vacuum brazing.
Inert-gas brazing using caesium-containing fluxes i s also possible here to a limited extent. Inert-gas brazin g using caesium-containing fluxes is especially simplified by the alloying fraction of magnesium not exceeding 0.8 wt.°.
In addition, with a low Mg content up to a maximum of 0.3 wt.o, the aluminium alloy according to the invention i_s readily suitable for inert-gas brazing using non-corrosive fluxes since a reaction with the fluxes only takes place to a limited extent and the use of more expensive caesium-containing fluxes can be dispense d with.
A particularly advantageous embodiment of the aluminium alloy according to the invention is obtained whereb y after processing and brazing and after natural ageing for approximately 30 days at room temperature the aluminium alloy has particularly high strength values. This material property ensures a particularly inexpensive fabrication process since the natural ageing as part of the transport process already ensures a very good strength without further measures.
According to a second teaching of the present invention, the object derived and indicated above is solved according to the method by - a rollinuJ bar being cast from an aluminium alloy according to the invention in a conventional bar casting method, - the rolling bar being homogenised at 500 to 600°C for more than 6 h, especially for more than 12 h, and being hot-rolled at at least 400°C, preferably 450°C, to form a strip, wherein the final temperature during the hot rolling is at least 300°C, - the hot-rolled strip being cold-rolled .to final thickness and being then subjected to soft annealing at at least 300°C, preferably 350°C.
As a result of the homogenisation of the rolling bar cast by the conventional bar casting method at temperatures of 500 to 600°C for more than 6 hours, especially for more than 12 hours, it is achieved that even sluggishly diffusing elements such as manganese and chromium are precipitated in a finely dispersed fashion during cooling of the melt. As a result of the hot rolling at at least 400°C an optimised structure of the hot strip is produced with regard to the deformability and corrosion resistance where the final rolling temperature during hot rolling must be at least 300°C in order to achieve sufficient deformability of the rolling bar on the one hand and optimised structure formation during the hot rolling on the other hand. In this case, the hot strip final thickness can be less than 9 mm, for example. In order to facilitate the forming of the strip produced by the method according to the invention into pre-fabricated components for the heat exchangers, for example, fins, tubes or distributors, the strip which has been cold-rolled to a maximum final thickness of 2 mm by cold rolling is subjected to subsequent soft annealing at at least 300°C, preferably 350°C.
As a result of the combination of the alloy composition of the aluminium alloy in conjunction with the process features described previously, heat exchangers can be fabricated on the basis of conventional alloying elements (Mg, Si, Cu) which, after inert-gas brazing and natural ageing for about 30 days at room temperature, have yield points of RP~,2 >- 65 MPa and are thus particularly well-suited for the enormous loads in motor vehicles. In addition, inert-gas brazing without using caesium-containing fluxes can be used to fabricate the heat exchangers so that economical fabrication is possible.
If the hot rolling and/or cold rolling takes place in a reversing or unidirectional mode on single- or multiple-stand rollers, the method according to the invention can be carried out using conventional means and devices with regard to the reducing rolling.
A particularly high process safety during brazing of the heat exchanger can be achieved by cladding the rolling bar with an aluminium solder after homogenising. The aluminium strip fabricated from this rolling bar has a uniform layer of aluminium solder which during brazing, results in particularly homogeneous and uniform brazed joints, for example, between the fins, tubes and distributors of the heat exchanger. If only one side of the aluminium strip according to the invention is clad with an aluminium solder, the other side can be cla d or coated with an alloy serving as corrosion protectio n, for example.
Advantageously used as aluminium solder is an aluminium alloy having a silicon content of 6-13 wt. o, especi ally an AlSi7 or A1Si10 alloy, which during inert-gas brazing have a particularly good wetting capacity with aluminium solder with regard to the oxide layers remaining in non-oxidising atmospheres on the components of the heat exchanger to be brazed.
Finally, the object derived and indicated above is solved according to a third teaching of the present invention by an aluminium strip or sheet for fabricating heat exchangers which is produced by the method according to the invention. As has already been stated, an aluminium strip or sheet produced by the method according to the invention has improved strength values, especially yield point, after natural ageing following brazing so that the wall thicknesses of the heat exchanger can be further reduced. In addition, inert-gas brazing using non-corrosive fluxes can be used to fabricate the heat exchangers without using caesium-containing fluxes.
The aluminium strip or sheet advantageously has a maximum thickness of 2 mm, especially 1 mm. As a result of the higher strength compared with conventional materials, when using the aluminium strip according to the invention, the strip thickness can be further reduced and thus material can be saved during the fabrication of heat exchangers and a further reduction in the weight of the heat exchangers can be achieved. In this case, the - l~ -operating safety of the heat exchanger is not impaired, even at r~igher operating pressures, because of the higher strength of the aluminium alloy.
There are now a plurality of possibilities for configuring and further developing the cold age-hardenable aluminium alloy for heat exchangers according to the first teaching of the invention, the method for producing a cold age-hardenable aluminium strip for heat exchangers according to the second teaching of the invention and the aluminium strip or sheet according to the inUention for fabricating heat exchangers according to the third teaching of the invention. For this purpose, for example, reference is made on the one hand to the claims subordinated to claims l, 5 and 9, on the other hand to the description of an exemplary embodiment of a method for fabricating a cold age-hardenable aluminium strip for heat exchangers according to the second teaching of the invention in conjunction with the drawing.
In the drawing the single figure is a schematic diagram showing the production path for implementing an exemplary embodiment of a method for fabricating a cold age-hardenable aluminium strip for heat exchangers according to the second teaching of the invention.
The production path shown in the single figure comprises the bar casting 1 from an aluminium alloy in a first step. In this case, the aluminium alloy of the exemplary embodiment has the following alloying components in wt.%
- 1i -0 < Si <-0.
. 70 60 0, ~
0.12 <_ Fe <-0.30, 0.08 <- Cu -<0.20%, 0.04%<- Mn < 0.080, 0.120< Mg <-0.300, Cr < 0.050, Zn < 0.050, 0.080<- Ti < 0.20a, B < 50 ppm, unavoidable accompanying elements to a maximum of 0.03° and to a maximum of 0.1~ in total and aluminium as the remainder.
The low boron content of 50 ppm maximum improves the recyclability of the aluminium alloy. The rolling bars cast using the DC method from the aluminium alloy just described are then homogenised in a homogenisation stage 2. Particularly good results with regard to the homogenisation of the rolling bar were achieved at a temperature of 575°C for more than 6 h, especially 12 h.
Following homogenisation the rolling bars are then hot-rolled on a tandem stand 3a to a thickness of 7 mm, for example, wherein in particular the final temperature during hot rolling must be higher than 300°C, preferably 330°C, in order to ensure optimised structure formation during the hot rolling. Alternatively, however, the hot rolling can be carried out on a reversing stand 3 and wound onto a reel which is not shown and hot rolling in the tandem stand 3a can be dispensed with. The subsequent cold rolling to a final thickness of about 1 mm takes place on single- or multiple-stand rollers 4. Dike the hot rolling the cold rolling can alternatively also be - i~ -carried out in reversing mode on a reversing stand. As a result of final soft annealing at about 350°C in a batch furnace 5, the aluminium strip is converted to a st ate of lowest possible strength and high elongation to facilitate subsequent forming work during fabrication of the heat exchanger components.
Alternatively to the exemplary embodiment of the method according to the invention for producing a strip for heat exchangers which has just been described, after homogenisation in the homogenisation stage 2 the rolling bar can be clad with an aluminium solder, for example of an AlSi7 or AlSilO alloy, to avoid subsequent application of an aluminium solder before the brazing of the heat exchangers fabricated from the strip according to the invention. For this purpose the rolling bar must be heated to an initial rolling temperature of at least 400°C, preferably 450°C, before the hot rolling. When brazing heat exchangers fabricated from aluminium strip or sheet according to the invention, especially when using inert-gas brazing particularly high strength values of the heat exchanger, in particular values for the yield point of RPo,2 >- 65 MPa can be achieved without using caesium-containing fluxes at temperatures up to 600°C and typical cooling rates of 30°C/min from 600°C to 200°C as well as natural ageing of about 30 days at room temperature after brazing. The cooling from 200°C to room temperature need not to take place in an exactly defined manner.
The invention relates to a cold age-hardenable aluminium alloy for heat exchangers, a method for producing a cold age-hardenable aluminium strip and an aluminium strip or sheet.
Heat exchangers consisting of aluminium or aluminium alloys are increasingly being used in the automobile field. In this case, the use of aluminium instead of the previously commonly used nonferrous metal heat exchangers has almost halved the weight of heat exchangers with comparable size and performance. Heat exchangers of aluminium or an aluminium alloy are nowadays used in the motor vehicle mainly for cooling the cooling water, oil and in air-conditioning systems. Heat exchangers f or motor vehicles are usually made of aluminium strips or sheets, the individual pre-fabricated components of the heat exchanger such as fins, tubes and distributors for example, being joined together by brazing. The loads acting in practical use on components thus manufactured and built into motor vehicles as a result of intermittent vibrations, more sustained vibrations, corrosion attack and similar are considerable. This particularly applies to the fins via which the heat is removed. Despite the considerable loads and increasing operating pressures of the heat exchangers in motor vehicles, there continues to be a trend towards saving weight in motor vehicles and therefore towards a further reduction in the wall thickness of the heat exchanger. However, this results in further increasing strength requirements for the aluminium alloy of the heat exchangers, especially after brazing. On the one hand, vacuum brazing without flux and inert-gas brazing using non-corrosive fluxes are available for brazing heat exchangers. The cold age-hardenable aluminium alloys used so far for the vacuum brazing of heat exchangers, for example, the aluminium alloy AA6063 (AlMgO, ?Si), AA6061 (AlMglSiCu) or AA6951 (AlMgO, 6SiCu), have relatively high magnesium contents in order, on the one hand, to prevent any oxidation of the molten aluminium solder on the components to be brazed as a result of "gettering" during the brazing process in vacuum and thereby ensure a perfect brazed joint without flux and on the other hand, to achieve high strength values of the brazed heat exchangers during natural ageing after brazing. A disadvantage with this method however is that it is cost-intensive to maintain the gas protection and the purity requirement for the components to be soldered. The alternative inert-gas brazing (also called CAB - controlled atmosphere brazing) certainly requires less expenditure under these aspects and additionally makes it possible to achieve up to 200 shorter brazing cycles but it is not possible to use the aluminium alloy having high magnesium contents known from vacuum brazing since the magnesium reacts with the non-corrosive fluxes during the brazing. This can only be prevented by using more expensive caesium-containing fluxes. It is furthermore possible to use high-copper-content aluminium alloys (Cu content > 0.50) which however tend to form heat cracks during casting and thus impose increased requirements on the casting of the rolling bars which should be considered to be critical from economic aspects. In addition, at elevated Cu i contents there is a risk of sensitivation for pitting or grain-boundary corrosion if copper is present in suitably precipitated form in the structure. Finally, in i:~ert-gas brazing an aluminium alloy with an intermediate cladding can be used as a diffusion barrier layer so that a cold age-hardenable aluminium alloy with relatively high magnesium contents is used as core material. Howev a r, intermediate cladding with a diffusion barrier lave r is associated with additional costs so that economica 1 production of heat exchangers likewise cannot be achieved.
The fabrication of heat exchangers by brazing of components consisting of the aforementioned aluminium alloys is known, for example, from US Patent Specification US 4,214,925.
Starting from the previously indicated prior art, it is thus the object of the present invention to provide a cold age-hardenable aluminium alloy for heat exchangers, a method for producing an aluminium strip for heat exchangers and a corresponding aluminium strip or sheet which has high strength values after natural agein g following brazing.
According to a first teaching of the present invention, the object derived and indicated above is solved f or an aluminium alloy by said aluminium alloy having the following alloying components in wt. o:
Si -<< 0.70 0.1% <- Mg < 1%
Fe <-0.30 0.080 < Cu < 0.20 Ti -<0.20 Mn -<<0.1%
Cr <-0.1o ~n <- 0.1%, unavoidable accompanying elements individually to a maximum of O.lo and in total to a maximum of 0.150 and aluminium as the remainder.
It has surprisingly been shown that heat exchangers consisting of an aluminium alloy containing the alloying fractions specified above, after natural ageing at room temperature following brazing, have the necessary strength for use in motor vehicles, especially the yield point RP~;,2, without further heat treatments being necessary. The reason for this is the combination of the Si and Mg contents according to the invention which form finely distributed precipitates of the type Mg2Si in the aluminium alloy according to the invention and result in an increase in strength as a result of natural ageing at room temperature. This increase in strength by natural ageing is further improved by adding copper in the claimed range of 0.08 wt.o to 0.2 wt. o.
Limiting the Fe content to a maximum of 0.3 wt.% ensures that Si is present in the aluminium alloy in a dissolved state. Furthermore, the low Cu contents of 0.2 wt.o maximum on the one hand ensure that the increase in strength during natural ageing can be increased and on the other hand, this limitation of the Cu content reduces the sensitivity of the strength of the aluminium alloy to the cooling rate after brazing. Likewise, the Mn content must be limited to a maximum of 0.1 wt.o to limit the dependence of the strength of the aluminium alloy on the cooling rate after brazing. In contrast, Cr contents of 0.1 wt.o maximum increase the strength and the corrosion resistance of the aluminium alloy according to the invention. In addition, a Ti content of 0.2 wt.% maximum has a positive effect on the resistance to corrosion of the aluminium alloy according to the invention since the Ti alloying element contributes to the grain refining of the structure of the aluminium alloy and thus makes the corrosion attack uniform. In order to avoid the negative effect of zinc on the corrosion of the aluminium alloy according to the invention, the 2n content must be restricted to a maximum of 0.1 wt. o.
According to a first advantageous embodiment, the strength of the aluminium alloy according to the invention can be further increased by natural ageing after brazing by the aluminium alloy containing Si, Mg and Cu as the principal alloying elements.
In order to avoid softening of the components of a heat exchanger to be brazed during brazing, it is advantageous for carrying out a perfect brazing process if the solidus temperature of the aluminium alloy does not go below 610°C
since brazing is usually carried out at temperatures up to 600°C. According to the invention this is achieved by the total of the alloying fractions of Si, Mg and Cu not exceeding 1.2 wt. o. In this-case, alloying elements generally bring about a reduction in the solidus temperature where Si causes a reduction in the solidus temperature of the aluminium alloy a factor of 1.2 greater than Mg and Mg in turn causes a reduction in the solidus temperature a factor of 3.5 more effective than Cu.
This does not apply to the alloying element Ti so that an increase in the solidus temperature of the aluminium alloy according to the invention can be achieved b y the aluminium alloy having Ti as an alloying component.
If the upper limit of the claimed alloy is exhauste d for magnesium, the brazing of heat exchangers fabricate d from this alloy is preferably effected by vacuum brazing.
Inert-gas brazing using caesium-containing fluxes i s also possible here to a limited extent. Inert-gas brazin g using caesium-containing fluxes is especially simplified by the alloying fraction of magnesium not exceeding 0.8 wt.°.
In addition, with a low Mg content up to a maximum of 0.3 wt.o, the aluminium alloy according to the invention i_s readily suitable for inert-gas brazing using non-corrosive fluxes since a reaction with the fluxes only takes place to a limited extent and the use of more expensive caesium-containing fluxes can be dispense d with.
A particularly advantageous embodiment of the aluminium alloy according to the invention is obtained whereb y after processing and brazing and after natural ageing for approximately 30 days at room temperature the aluminium alloy has particularly high strength values. This material property ensures a particularly inexpensive fabrication process since the natural ageing as part of the transport process already ensures a very good strength without further measures.
According to a second teaching of the present invention, the object derived and indicated above is solved according to the method by - a rollinuJ bar being cast from an aluminium alloy according to the invention in a conventional bar casting method, - the rolling bar being homogenised at 500 to 600°C for more than 6 h, especially for more than 12 h, and being hot-rolled at at least 400°C, preferably 450°C, to form a strip, wherein the final temperature during the hot rolling is at least 300°C, - the hot-rolled strip being cold-rolled .to final thickness and being then subjected to soft annealing at at least 300°C, preferably 350°C.
As a result of the homogenisation of the rolling bar cast by the conventional bar casting method at temperatures of 500 to 600°C for more than 6 hours, especially for more than 12 hours, it is achieved that even sluggishly diffusing elements such as manganese and chromium are precipitated in a finely dispersed fashion during cooling of the melt. As a result of the hot rolling at at least 400°C an optimised structure of the hot strip is produced with regard to the deformability and corrosion resistance where the final rolling temperature during hot rolling must be at least 300°C in order to achieve sufficient deformability of the rolling bar on the one hand and optimised structure formation during the hot rolling on the other hand. In this case, the hot strip final thickness can be less than 9 mm, for example. In order to facilitate the forming of the strip produced by the method according to the invention into pre-fabricated components for the heat exchangers, for example, fins, tubes or distributors, the strip which has been cold-rolled to a maximum final thickness of 2 mm by cold rolling is subjected to subsequent soft annealing at at least 300°C, preferably 350°C.
As a result of the combination of the alloy composition of the aluminium alloy in conjunction with the process features described previously, heat exchangers can be fabricated on the basis of conventional alloying elements (Mg, Si, Cu) which, after inert-gas brazing and natural ageing for about 30 days at room temperature, have yield points of RP~,2 >- 65 MPa and are thus particularly well-suited for the enormous loads in motor vehicles. In addition, inert-gas brazing without using caesium-containing fluxes can be used to fabricate the heat exchangers so that economical fabrication is possible.
If the hot rolling and/or cold rolling takes place in a reversing or unidirectional mode on single- or multiple-stand rollers, the method according to the invention can be carried out using conventional means and devices with regard to the reducing rolling.
A particularly high process safety during brazing of the heat exchanger can be achieved by cladding the rolling bar with an aluminium solder after homogenising. The aluminium strip fabricated from this rolling bar has a uniform layer of aluminium solder which during brazing, results in particularly homogeneous and uniform brazed joints, for example, between the fins, tubes and distributors of the heat exchanger. If only one side of the aluminium strip according to the invention is clad with an aluminium solder, the other side can be cla d or coated with an alloy serving as corrosion protectio n, for example.
Advantageously used as aluminium solder is an aluminium alloy having a silicon content of 6-13 wt. o, especi ally an AlSi7 or A1Si10 alloy, which during inert-gas brazing have a particularly good wetting capacity with aluminium solder with regard to the oxide layers remaining in non-oxidising atmospheres on the components of the heat exchanger to be brazed.
Finally, the object derived and indicated above is solved according to a third teaching of the present invention by an aluminium strip or sheet for fabricating heat exchangers which is produced by the method according to the invention. As has already been stated, an aluminium strip or sheet produced by the method according to the invention has improved strength values, especially yield point, after natural ageing following brazing so that the wall thicknesses of the heat exchanger can be further reduced. In addition, inert-gas brazing using non-corrosive fluxes can be used to fabricate the heat exchangers without using caesium-containing fluxes.
The aluminium strip or sheet advantageously has a maximum thickness of 2 mm, especially 1 mm. As a result of the higher strength compared with conventional materials, when using the aluminium strip according to the invention, the strip thickness can be further reduced and thus material can be saved during the fabrication of heat exchangers and a further reduction in the weight of the heat exchangers can be achieved. In this case, the - l~ -operating safety of the heat exchanger is not impaired, even at r~igher operating pressures, because of the higher strength of the aluminium alloy.
There are now a plurality of possibilities for configuring and further developing the cold age-hardenable aluminium alloy for heat exchangers according to the first teaching of the invention, the method for producing a cold age-hardenable aluminium strip for heat exchangers according to the second teaching of the invention and the aluminium strip or sheet according to the inUention for fabricating heat exchangers according to the third teaching of the invention. For this purpose, for example, reference is made on the one hand to the claims subordinated to claims l, 5 and 9, on the other hand to the description of an exemplary embodiment of a method for fabricating a cold age-hardenable aluminium strip for heat exchangers according to the second teaching of the invention in conjunction with the drawing.
In the drawing the single figure is a schematic diagram showing the production path for implementing an exemplary embodiment of a method for fabricating a cold age-hardenable aluminium strip for heat exchangers according to the second teaching of the invention.
The production path shown in the single figure comprises the bar casting 1 from an aluminium alloy in a first step. In this case, the aluminium alloy of the exemplary embodiment has the following alloying components in wt.%
- 1i -0 < Si <-0.
. 70 60 0, ~
0.12 <_ Fe <-0.30, 0.08 <- Cu -<0.20%, 0.04%<- Mn < 0.080, 0.120< Mg <-0.300, Cr < 0.050, Zn < 0.050, 0.080<- Ti < 0.20a, B < 50 ppm, unavoidable accompanying elements to a maximum of 0.03° and to a maximum of 0.1~ in total and aluminium as the remainder.
The low boron content of 50 ppm maximum improves the recyclability of the aluminium alloy. The rolling bars cast using the DC method from the aluminium alloy just described are then homogenised in a homogenisation stage 2. Particularly good results with regard to the homogenisation of the rolling bar were achieved at a temperature of 575°C for more than 6 h, especially 12 h.
Following homogenisation the rolling bars are then hot-rolled on a tandem stand 3a to a thickness of 7 mm, for example, wherein in particular the final temperature during hot rolling must be higher than 300°C, preferably 330°C, in order to ensure optimised structure formation during the hot rolling. Alternatively, however, the hot rolling can be carried out on a reversing stand 3 and wound onto a reel which is not shown and hot rolling in the tandem stand 3a can be dispensed with. The subsequent cold rolling to a final thickness of about 1 mm takes place on single- or multiple-stand rollers 4. Dike the hot rolling the cold rolling can alternatively also be - i~ -carried out in reversing mode on a reversing stand. As a result of final soft annealing at about 350°C in a batch furnace 5, the aluminium strip is converted to a st ate of lowest possible strength and high elongation to facilitate subsequent forming work during fabrication of the heat exchanger components.
Alternatively to the exemplary embodiment of the method according to the invention for producing a strip for heat exchangers which has just been described, after homogenisation in the homogenisation stage 2 the rolling bar can be clad with an aluminium solder, for example of an AlSi7 or AlSilO alloy, to avoid subsequent application of an aluminium solder before the brazing of the heat exchangers fabricated from the strip according to the invention. For this purpose the rolling bar must be heated to an initial rolling temperature of at least 400°C, preferably 450°C, before the hot rolling. When brazing heat exchangers fabricated from aluminium strip or sheet according to the invention, especially when using inert-gas brazing particularly high strength values of the heat exchanger, in particular values for the yield point of RPo,2 >- 65 MPa can be achieved without using caesium-containing fluxes at temperatures up to 600°C and typical cooling rates of 30°C/min from 600°C to 200°C as well as natural ageing of about 30 days at room temperature after brazing. The cooling from 200°C to room temperature need not to take place in an exactly defined manner.
Claims (13)
1. a cold age-hardenable aluminium alloy for heat exchangers, characterised in that the aluminium alloy comprises the following alloying components in wt.%:
Si <= 0.7%
0.1% <= Mg <= 1%
Fe <= 0.3%
0.08% <= Cu <= 0.2%
Ti <= 0.2%
Mn <= 0.1%
Cr <= 0.1%
Zn <= 0.1%, unavoidable accompanying elements individually to a maximum of 0.1% and in total to a maximum of 0.15%
and aluminium as the remainder.
Si <= 0.7%
0.1% <= Mg <= 1%
Fe <= 0.3%
0.08% <= Cu <= 0.2%
Ti <= 0.2%
Mn <= 0.1%
Cr <= 0.1%
Zn <= 0.1%, unavoidable accompanying elements individually to a maximum of 0.1% and in total to a maximum of 0.15%
and aluminium as the remainder.
2. The cold age-hardenable aluminium alloy according to claim 1, characterised in that the aluminium alloy contains Si, Mg and Cu as principal alloying elements.
3. The cold age-hardenable aluminium alloy according to claim 1 or claim 2, characterised in that the total of the alloying fractions of Si, Mg and Cu does not exceed 1.2 wt.%.
4. The aluminium alloy according to any one of claims 1 to 3, characterised in that the aluminium alloy comprises Ti as an alloying component.
5. The aluminium alloy according to any one of claims 1 to 4, characterised in that the alloying fraction of Mg does not exceed 0.8 wt.%.
6. The aluminium alloy according to any one of claims 1 to 4, characterised in that the alloying fraction of Mg does not exceed 0.3 wt%.
7. The aluminium alloy according to any one of claims 1 to 6, characterised in that after processing and brazing and after natural ageing for approximately 30 days at room temperature the aluminium alloy has particularly high strength values.
8. A method for producing a cold age-hardenable aluminium strip for heat exchangers from an aluminium alloy according to any one of claims 1 to 7, characterised in that - a rolling bar is cast in a conventional bar casting method, - the rolling bar is homogenised at 500 to 600°C
for more than 6 h, especially for more than 12 h, - the rolling bar is hot-rolled at at least 400°C, preferably 450°C, to form a strip, wherein the final temperature during the hot rolling is at least 300°C, - the hot-rolled strip is cold-rolled to final thickness and is then subjected to soft annealing at at least 300°C, preferably 350°C.
for more than 6 h, especially for more than 12 h, - the rolling bar is hot-rolled at at least 400°C, preferably 450°C, to form a strip, wherein the final temperature during the hot rolling is at least 300°C, - the hot-rolled strip is cold-rolled to final thickness and is then subjected to soft annealing at at least 300°C, preferably 350°C.
9. The method according to claim 8, characterised in that the hot rolling and/or cold rolling takes place in a reversing or unidirectional mode on single- or multiple-stand rollers.
10. The method according to claim 8 and claim 9, characterised in that after homogenising the rolling bar is clad with an aluminium solder.
11. The method according to claim 10, characterised in that an aluminium alloy having a silicon content of 6-13 wt.%, especially an AlSi7 or AlSi10 alloy, is used as aluminium solder.
12. An aluminium strip or sheet for manufacturing heat exchanges consisting of an aluminium alloy according to any one of claims 1 to 7, especially manufactured using a method according to any one of~
claims 8 to 11.
claims 8 to 11.
13. The aluminium strip or sheet according to claim 12, characterised in that the aluminium strip or sheet has a maximum thickness of 2 mm, preferably 1 mm.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP03016970.0 | 2003-07-25 | ||
| EP03016970 | 2003-07-25 | ||
| EP03029964A EP1505163A3 (en) | 2003-07-25 | 2003-12-30 | High strength Aluminium alloy for use in a heat exchanger |
| EP03029964.8 | 2003-12-30 | ||
| PCT/EP2004/008359 WO2005010223A1 (en) | 2003-07-25 | 2004-07-26 | Resistant alloy for heat exchangers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2533428A1 true CA2533428A1 (en) | 2005-02-03 |
Family
ID=33553812
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002533428A Abandoned CA2533428A1 (en) | 2003-07-25 | 2004-07-26 | High-strength alloy for heat exchangers |
Country Status (8)
| Country | Link |
|---|---|
| EP (2) | EP1505163A3 (en) |
| JP (1) | JP2007500784A (en) |
| KR (1) | KR20060030910A (en) |
| AU (1) | AU2004259849A1 (en) |
| BR (1) | BRPI0412907A (en) |
| CA (1) | CA2533428A1 (en) |
| EA (1) | EA200600211A1 (en) |
| WO (1) | WO2005010223A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102008059450A1 (en) * | 2008-11-28 | 2010-06-02 | Behr Gmbh & Co. Kg | Aluminum strip, soldering component, manufacturing method and heat exchanger and use |
| CN101660883B (en) * | 2009-09-04 | 2011-10-26 | 东莞市奥达铝业有限公司 | Manufacturing method of vehicle aluminum alloy radiating fin |
| KR101453427B1 (en) * | 2012-04-20 | 2014-10-23 | 한국생산기술연구원 | An inner liner and pin material for heat exchanger |
| CN115427188B (en) * | 2020-04-08 | 2023-12-19 | 斯佩拉有限公司 | Aluminum material, method for thermally joining parts, use of aluminum material therein, and welded part |
| DE112022004812T5 (en) | 2021-11-04 | 2024-07-18 | Uacj Corporation | ALUMINUM ALLOY BRAZING SHEET AND METHOD OF PRODUCING THE SAME |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1335309A (en) * | 1970-12-21 | 1973-10-24 | Olin Corp | Heat exchanger |
| FR2185946A5 (en) * | 1972-05-23 | 1974-01-04 | Chausson Usines Sa | |
| FR2186028A5 (en) * | 1972-05-23 | 1974-01-04 | Cegedur | |
| JPS5461015A (en) * | 1977-10-25 | 1979-05-17 | Kobe Steel Ltd | Manufacture of aluminum-soldered fin heat exchanger |
| JPH05263172A (en) * | 1992-03-17 | 1993-10-12 | Furukawa Alum Co Ltd | Aluminum alloy for fin material of heat exchanger |
| JP3495263B2 (en) * | 1998-09-16 | 2004-02-09 | 昭和電工株式会社 | Method for producing Al-Mg-Si alloy sheet excellent in thermal conductivity and strength |
| EP1158063A1 (en) * | 2000-05-22 | 2001-11-28 | Norsk Hydro A/S | Corrosion resistant aluminium alloy |
-
2003
- 2003-12-30 EP EP03029964A patent/EP1505163A3/en not_active Withdrawn
-
2004
- 2004-07-26 CA CA002533428A patent/CA2533428A1/en not_active Abandoned
- 2004-07-26 WO PCT/EP2004/008359 patent/WO2005010223A1/en not_active Application Discontinuation
- 2004-07-26 KR KR1020067001679A patent/KR20060030910A/en not_active Application Discontinuation
- 2004-07-26 JP JP2006521503A patent/JP2007500784A/en not_active Withdrawn
- 2004-07-26 BR BRPI0412907-5A patent/BRPI0412907A/en not_active Application Discontinuation
- 2004-07-26 AU AU2004259849A patent/AU2004259849A1/en not_active Abandoned
- 2004-07-26 EA EA200600211A patent/EA200600211A1/en unknown
- 2004-07-26 EP EP04763503A patent/EP1649070A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| AU2004259849A1 (en) | 2005-02-03 |
| EP1649070A1 (en) | 2006-04-26 |
| WO2005010223A1 (en) | 2005-02-03 |
| EA200600211A1 (en) | 2006-08-25 |
| BRPI0412907A (en) | 2006-09-26 |
| JP2007500784A (en) | 2007-01-18 |
| KR20060030910A (en) | 2006-04-11 |
| EP1505163A3 (en) | 2005-02-16 |
| EP1505163A2 (en) | 2005-02-09 |
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